1. Field of the Invention
The present invention relates to an optical disk on and/or from which information is recorded and/or reproduced in the form of recording pits by effectively utilizing concave and convex patterns, a modulation of reflective index, a magneto-optical effect or the like, for example.
2. Description of the Related Art
In optical disks such as a compact disc (CD) and a mini-disk (MD) in which recording pits are formed by effectively utilizing concave and convex portions formed on the disk surface, the phase change, the magneto-optical effect or the like, a rotational jitter must be reduced by rotating the disk with high accuracy to thereby suppress a read-out error.
In the case of a CAV (constant angular velocity) system optical disk, a rotation synchronizing signal is obtained not from the optical disk but from an encoder pulse of a spindle that rotates the optical disk. In the case of a CLV (constant linear velocity) system optical disk, a rotational speed of a spindle is controlled such that a synchronizing signal of a header portion recorded on the optical disk in advance may have a predetermined frequency.
General optical disks have only several 10 s of sectors formed in one track and therefore a frequency of the synchronizing signal becomes less than about 1 kHz. Therefore, even when the rotational speed of the spindle is controlled with higher accuracy, the rotational jitter cannot be suppressed sufficiently. As a result, a buffer area between the sectors must be increased in area, which makes it impossible to increase a storage capacity of the optical disk.
When a video signal is stored in the optical disk in the form of an analog signal, a rotation synchronizing signal of the optical disk has a frequency of 30 kHz in view of a recording density relationship because the synchronizing signal of the NTSC video signal has a frequency of 30 kHz. At that time, if the optical disk is rotated at the CLV mode, then the buffer area between the sectors is increased because the rotational jitter must be suppressed, thereby making it impossible to realize the increase of the storage capacity of the optical disk.
Further, when a wide band signal such as an HD (high definition) (MUSE) signal is recorded on and reproduced from the optical disk, a data transfer rate must be increased (band of the recording signal must be widened in the case of the analog signal). In the single channel system, as means for increasing the data transfer rate, it is proposed to increase a relative speed between the optical disk and the laser beam. However, when a recording density of the optical disk is increased, a laser beam having a short wavelength is required or an optical disk made of a perfectly new material is also required. In addition, a laser beam of a larger intensity is needed to increase the above relative speed.